This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Antibody phage display is a useful method of developing fully human monoclonal antibodies against both known and novel tumor antigens. We have obtained over 70 phage antibodies that specifically bind to and internalize within prostate cancer cells. Uncovering their molecular identities will lead to better understanding of cancer biology and better assessment of these molecules as targets for targeted immunotherapeutics. We propose to use immunoprecipitation and tandem mass spectrometry to obtain peptide sequences of antigens targeted by the antibodies.